1. Field of the Invention
The invention relates to the field of rapid synthesis of metal oxide nanoparticles and more particularly nanowires at low temperatures utilizing oxygen plasma for rapid growth and optimizing the density of the neutral oxygen atoms in the plasma for different materials to maximize growth parameters.
2. Description of the Prior Art
Metal oxide nanoparticles have great potential for application in medicine, biotechnology, microelectronics and chemical industry. Nanostructural materials have typical side dimension below 200 nm, while the longitudinal dimension is often orders of magnitude larger. They appear in different forms including spheres, tubes, wires, and more complex shape (onion-like, stars, spikes etc.) The characteristics of nanostructured materials are often different from characteristics of parent bulk materials. Many nanostructured materials are made from carbon, but in recent years nanomaterials made from metals, insulators, semiconductors and other materials have been reported. Nanomaterials made from the following elements and their compounds have been reported: Ag, Au, Pt, Fe, Ni, Co, Si, Pd, Mo, Ga, O, S, N.
A variety of methods for synthesis nanomaterials have been reported. Many are based on deposition from the vapor phase. A popular method is also the growth by using small islands of low melting point materials deposited on substrates. Most methods are based on application of conditions close to thermodynamic equilibrium. Non equilibrium methods often apply electrical discharges where the material that is to be deposited is evaporated and partially ionized. A classical discharge is an electric arc. A typical temperature in the arc is several 1000K, so solid materials placed into the ac are evaporated. The vapor is condensed on appropriate substrate and under certain conditions (temperature, pressure, morphology) they condensate in the form of nanostructures. Another commonly used method is based on classical heating in a furnace. In this case the material is evaporated and condensed on cooled substrate so that nanomaterials are formed. Different catalysts are often applied in order to facilitate one-dimensional growth. The deposition rate is often small due to limitation of the process: at higher deposition rates the growth unisotropy is usually lost.
Some metals such as niobium are often used as a catalyst (ie condensation, nuclei) during vapor phase deposition of nanomaterials suitable for storage high quantity of hydrogen (WO001865821), (WO9965821), (WO9965821). In such examples hydrocarbons are passed through a discharge where they are dehydrogenized. The modified hydrocarbons are condensed on substrates and nanomaterial is formed. The dimensions as well as structure of such carbon nanoparticles depend on discharge conditions. Similar procedure is used in (US Patent Publication 200211494, TW444067, WO0234669, EP1046613, WO0185612, EP1129990, WO9842621, WO03062146, and US Patent Publication 20030082094). Plasma is also used for functionalization of the surface of carbon nanostructured materials, such as tubes and wires to improve electrical as well as mechanical properties. Such materials may be used in cold emitter devices or atomic force microscopes (WO0180273, WO0131673).
Apart from carbon nanowires, (US Patent Publication 2003044608, U.S. Pat. No. 6,465,132, US Patent Publication 2002117659, US Patent Publication 20010511367, WO03057620), reports have been on polymer nanowires for pharmaceutical application (US Patent Publication 2002055239, (EP1215199, EP1209695). Other materials suitable for synthesis of nanowires include Si, Ge, SiO (US Patent Publication 2002129761), Au (U.S. Pat. No. 6,413,880), Bi, Ga, In (U.S. Pat. No. 6,359,288), Si (U.S. Pat. No. 6,313,015), Pd, Cu, Au, Ni, Pt, (WO03008954), Pt, Fe, Co, Ni, Au, Ag, Pt, Co, their oxides in alloys including FeCo, NiFe, AuAg, CuNi (US Patent Publication 2002187504), Si and SiGe (US Patent Publication 2002175408, Bi (US Patent Publication 200217590). Plasma is also used for synthesis dust nanoparticles (WO03095360), for instance TiO2(WO02086179).
All of the patents cited above claim synthesis of nanomaterials that is either carried out at- or close to-thermodynamic equilibrium, or at non-equilibrium from the vapor phase and application of appropriate catalyst US Patent Publication 20030039602. There is no report on synthesis nanomaterials directly from the solid material under non-equilibrium conditions, apart from the current co-inventors Slovenia Patent SI21136 published on Aug. 31, 2003 and hereby incorporated by reference.